In a conventional technique for gathering sunlight without using a driving unit, sunlight is diffused and introduced indoors or into a greenhouse by using a light transmitting thin plate having various ridges on its surface or a film-like structure on the surface of which a lot of ridges of various sectional configurations are arranged closely and in parallel. Further, by using a similar diffusion structure, light flux from a fluorescent lamp is diffused to thereby achieve a reduction in glare.
However, in the diffusion by such a light diffusion structure, the distribution of the diffused light is greatly influenced by the direction of the incident light. Also in the invention as disclosed in JP 7-296617 by the present applicant, there is involved a great unevenness in the distribution of the diffused light depending upon the angle of incidence, as stated in the embodiment section of the specification. Thus, in a system in which sunlight is taken indoors to substantially reduce the illumination power in the daytime, it is impossible to sufficiently solve the problem of the unevenness in indoor sunlight distribution. For the same reason, there is a limitation in the application of such a system to a greenhouse. Further, when applied to a fluorescent lighting equipment, such a system is not enough to eliminate the glare of the fluorescent lamp.